Pryophoric devices used in such a lighter generally comprise an abrasive striker wheel coacting with a flint which is pressed against the striker-wheel surface by a spring. Rapid rotation of the wheel generates sparks igniting a flow of gas emitted by the source upon the simultaneous opening of a normally closed shut-off valve. Such rapid rotation can usually be brought about when the striker wheel is acted upon by a stored force, e.g. that of a spring which is stressed by the closure of a lid and released when the lid is allowed to snap open. With direct manual actuation, however, special means must be provided to convert the user's finger pressure into the acceleration required. Such means conventionally may take the form of humps coacting with the wheel drive to provide a resistance necessitating the buildup of a certain force which imparts the desired rotation to the striker wheel upon overcoming that resistance. This type of mechanism, however, is generaly somewhat cumbersome and does not always operate satisfactorily.